Go to Dashboard > Settings > General, scroll down to Custom Login Image option and select Use my custom image as a logo (or header).
That way your login image will change to the one you select there - it’s not a theme specific feature. It’s a CP core feature (that is not present in WP ;P)
Wow thanks very much. Figures it would have to be that easy eh? Not sure how I overlooked that but its been awhile since I set up the settings so must be my ole timers kicking in.